The limited supplies of natural gas (methane) in the United States, together with its great usefulness, have provided the necessary incentive for the discovery and development of techniques to produce synthetic natural gas (SNG) by a reaction known as methanation. The methanation reaction generally involves the conversion of synthesis gas to methane and water in the presence of a suitable catalyst. Synthesis gas is a mixture of CO and hydrogen and can be produced by the gasification of coal with steam and oxygen. Suitable catalysts for methanation are described in the prior art and include iron, nickel and ruthenium, among others. The Bureau of Mines Report of Investigation 5137 entitled "Synthesis of Methane" by Murray Greyson et al (July 1955) reports that nickel is superior to iron and that the techniques of catalyst preparation determine to a large extent the process life of the nickel catalyst.
The nickel catalysts investigated by the Bureau and others are typically prepared by precipitating nickel salts such as nickel nitrate onto various supports such as alumina or kieselguhr. In addition to poor aging characteristics, prior art nickel catalysts suffer from their tendency to promote undesired side reactions such as the disproportionation of the CO to CO.sub.2 and the formation of carbon either by the decomposition of CO or the formation of higher molecular weight hydrocarbons which eventually deposit and form coke.
The inventors have discovered in accordance with their teachings in copending U.S. Ser. No. 532,848 now U.S. Pat. No. 3,947,483, entitled "Metal Chrysotile Methane Synthesis Catalyst", filed on Dec. 16, 1974, that an improved methanation catalyst comprises a crystalline layered complex metal silicate characterized as having repeating units having the structural formula: EQU [(1-x)Ni.sup.a +xRu.sup.b ].sub.n (OH).sub.4 Si.sub.2 O.sub.5.wH.sub.2 O
where x is a number from 0 to 1, this number expressing the atomic fraction of the metals nickel and ruthenium, a is the valence of nickel, b is the valence of ruthenium, n is a number equal in value to that defined by the ratio EQU 6/[a(1-x)+ bx]
and w is a number ranging from 0 to 4.
It has now been discovered in accordance with the invention that the efficiency of the nickel chyrsotile catalysts can be improved together with their thermal stability by the substitution of magnesium for a portion of the nickel in the nickel chrysotile catalysts.
Thus, in accordance with the invention, an improved process has been discovered for the production of methane which comprises contacting a charge stock comprising hydrogen and at least one carbon oxide selected from the group consisting of CO and CO.sub.2 wherein the molar ratio of hydrogen to combined carbon oxides is at least 2:1 under methanation conditions with a catalyst comprising a metal silicate characterized as having repeating units having the structrual formula: EQU [(1-x)Ni.sup.+2 +xMg+ 2].sub.3 (OH).sub.4 Si.sub.2 O.sub.5.wH.sub.2 O
where x is a number from 0.01 to 0.6, this number expressing the atomic fraction of the metals nickel and magnesium and w is a number ranging from 0 to 4.